US7254389B2 - Wireless link simulation with generic caching - Google Patents
Wireless link simulation with generic caching Download PDFInfo
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- US7254389B2 US7254389B2 US10/821,558 US82155804A US7254389B2 US 7254389 B2 US7254389 B2 US 7254389B2 US 82155804 A US82155804 A US 82155804A US 7254389 B2 US7254389 B2 US 7254389B2
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
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- H04W16/00—Network planning, e.g. coverage or traffic planning tools; Network deployment, e.g. resource partitioning or cells structures
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- This invention relates to the field of simulation systems, and in particular to a network simulator that is configured to model wireless networks.
- the simulation of networks to predict performance, identify bottlenecks, assess possible changes, and so on, is common in the art.
- parameters such as propagation delay, error rates, reliability, and so on, are fairly constant for a given communications link.
- wireless network In a wireless network, however, such parameters can vary substantially with time, particularly in a wireless network with mobile transceivers.
- the simulation of wireless transmissions requires, for example, the computation of a set of characteristics to determine whether a communication can take place between a transmitter and receiver, including, for example, the current distance between the transmitter and receiver, interference between the transmitter and receiver, the current power level of the transmitter, and so on. These characteristics also affect the determination of whether the receiver obtains a valid copy of the transmission, the degree of interference on other communications caused by the transmission, and other factors that are used to assess the overall performance of the network.
- the conventional simulation of a system is accomplished by generating sample events, then propagating each event from node to node in the system. That is, for example, consider an event that is a new message generated at node A and addressed to node B. Consider, also that node X is between nodes A and B.
- the transmitted message from node A is simulated as arriving at node X at some time after its transmission from A, then simulated as being processed by node X, incurring, for example, a queuing delay at node X, and a subsequent transmission to node B at a following time.
- the transmitted message from node X is simulated as arriving at node B at some time later, processed at node B, including queuing or other delays, as appropriate.
- the total delay time from transmission at node A to completed reception at node B can be determined.
- Other phenomena can also be modeled. For example, random requests for retransmissions can be generated based on simulated noise levels, increasing queue delays can be simulated based on increased traffic, and so on.
- the models of each node can be changed to determine the effect of the change on the system performance. For example, the propagation delay time between node A and B can be determined as a function of the size of buffers, or the type of processor, at node X, to determine whether changes should be made at node X.
- simulation is an iterative process of propagating simulated events and subsequent internal events caused by the simulated events
- a simulation of a moderately complex network can be extremely time consuming.
- An increase in the time required to simulate the propagation an event at a node can have a substantial effect on the time required to simulate a system.
- each transmission at a wireless node requires the aforementioned determination of potentially changing characteristics, the simulation of a wireless network is generally significantly slower than the simulation of a similar-size wired network.
- a simulation system that includes a cache structure that stores determined characteristics related to the propagation of an event. If a similar event occurs, and the factors affecting the determination of these characteristics have not changed, the characteristics associated with the new event are retrieved from the cache, rather than being re-determined from the underlying factors.
- the determined characteristics of one transceiver can be shared among all of the other transceivers. If the underlying factors are dependent upon geographic area, mobile transceivers that enter a geographic area having associated cached characteristics can use the cached characteristics of other transceivers that are, or had been, in the area.
- the cache process is structured to intercept a call to the routine that determines the characteristics, pass the call to the routine if the characteristics have not yet been determined for the given set of underlying factors, and store the results from the routine for potential subsequent use, the modifications to a simulation system to incorporate this caching feature should be minimal.
- FIG. 1 illustrates an example model of a wireless network for simulation using the principles of this invention.
- FIG. 2 illustrates an example flow diagram of a cache controller for simulating a communication network in accordance with this invention.
- FIG. 3 illustrates an example flow diagram of a simulation system in accordance with this invention.
- FIG. 4 illustrates an example block diagram of a simulation system with cache in accordance with this invention.
- the invention is presented in the context of a simulation system for wireless communication networks, because of the efficiencies that are realized in this application. Specifically, when simulating wireless communications where terrain effects play a role in determining the simulated effects of a communication, if long or moderate distances separate the receiver and transmitter, that minor differences in location of said transmitter and receiver do not play a substantial role in affecting the results. If the transmitter and receiver, for example, are separated by a few kilometers and the granularity of terrain information available to most simulators is on the order of meters or tens of meters, objects within the same “region” that communicate with objects in another region can “reuse” the terrain profile and effects of the terrain on the communication without substantial loss of accuracy.
- a preferred embodiment of this invention takes advantage of the above observation by allowing nodes in a cluster to share the terrain information derived from a first communication out of that cluster.
- the reuse of results is appropriate because even if the nodes are slightly separated from each other (or will be once one or more enter a particular region), the results are likely to be sufficiently accurate for the purposes of the simulation.
- FIG. 1 illustrates an example model of a wireless network for simulation using the principles of this invention.
- a base station B is configured to communicate with mobile transceivers 1 – 5 .
- This structure is presented for ease of understanding, and it will be evident to one of ordinary skill in the art that this invention is not limited to a network with a stationary base station.
- regions I–VI are intended to represent geographic regions relative to the base station B.
- each region represents an area within which receptions from base station B exhibit similar characteristics.
- the characteristics of receptions at transceivers 2 and 5 , each in region V are assumed to be substantially equivalent.
- the asymmetric nature of these example regions represent the irregularity of a base station's reception due to terrain, obstructions, reflections, and so on; in an easier-to-implement embodiment, regular and/or algorithmically determined regions can be defined, such as a grid structure, concentric rings, and so on.
- FIG. 1 illustrates, via the dashed arrow, a motion of the transceiver 1 from region II, through region V, and into region I.
- this is a simulated motion of a hypothetical transceiver 1 in the vicinity of a modeled base station B; however, for ease of presentation, the adjectives “simulated” and “hypothetical” will not be explicitly stated, except as required for clarity.
- transceiver 1 While the transceiver 1 is in region II, each of its communications with the base station B are assumed to be characteristically similar; while transceiver 1 is in region V, each of its communications with the base station B are assumed to be characteristically similar to the communications between transceivers 2 and 5 and the base station B; and while in region I, characteristically similar to the communications between transceiver 3 and the base station B.
- each of the regions are defined as regions of similar characteristics relative to the base station B, once a first communication with base station B occurs within a given region with a particular set of factors (such as transmit power, message length, and so on), and the effects of that communication determined (such as the likelihood of success, received noise level, propagation delay time, and so on), these same effects can be assumed to occur when another communication with a substantially similar set of factors occurs.
- a particular set of factors such as transmit power, message length, and so on
- the effects of that communication determined such as the likelihood of success, received noise level, propagation delay time, and so on
- the effects of each first occurrence of a simulated communication within a region with a particular set of factors are stored in a cache. Thereafter, when another communication within the same region with the same set of factors is simulated to occur, the effects of this communication is read from the cache. Assuming that retrieval of the effects from cache can be accomplished within the simulator more quickly than the original determination of the effects, substantial time savings can be achieved, due to the iterative nature of simulation systems. The overall time savings that will be achieved, however, is this cache-retrieval time savings less the overhead required to create and maintain the cache, including the time required to store each first communication to the cache.
- the region within which the communication occurs can be considered as yet another factor of the communication between each transceiver and the base station B.
- the communication profile of the base station B that defines each of the regions I–VI can be consider another factor of the communication between each transceiver and the base station B, or any base station having a similar profile.
- the similarity of the devices used for the communication provides a first-level determination of whether the communications may be occurring with similar underlying factors. That is, in this embodiment of the invention, the effects of a first communication between a transmitter and receiver with a particular set of factors are stored in cache, so that if another communication between a ‘similar’ transmitter and a ‘similar’ receiver occurs with a similar set of factors, the effects can be retrieved from cache.
- This embodiment effectively provides a hierarchical structure for determining whether two communications are similar: if the transmitters of each communication are not similar, or if the receivers of each communication are not similar, then the effects of each communication will not be assumed to be similar, regardless of the other factors that affect the communications. Further, or alternative, hierarchical structuring may be employed, such as a hierarchy based on transmit power levels. That is, if the transmit power levels of two communications are not similar, the effects of the communications are not assumed to be similar, regardless of the remaining factors that affect the communications.
- clustering is often used to determine and/or define similarities among objects or parameters, and the prior art is replete with techniques for clustering similar items.
- Numeric parameters for example, may be clustered by comparing the distance between different sample values relative to the overall variance of the all the sample values, closely spaced values being considered members of the same cluster.
- Quantizing, rounding, and other techniques that provide a common value to closely valued samples are also commonly used to define clusters of values. Note that as used in this application, the term quantizing is used to define a mapping of a set of ranges of values to a set of nominal values, without limitation on the techniques used to effect the mapping.
- Different transmitters that have similar transmission characteristics can be clustered as one of a plurality of transmitter clusters, and different receivers that have similar reception characteristics can be clustered as one of a plurality of receiver clusters.
- the same transmitter having adjustable transmission characteristics such as different transmit power options, can be a member of a variety of clusters, depending upon the given transmit power level; and the same receiver being in different transmitter regions can be a member of a variety of clusters, depending upon its current location.
- transmit clusters and receive clusters are defined such that communications from any transmitter within a given transmitter cluster to any receiver within a given receiver cluster will exhibit the same effects as any other communication from the given transmitter cluster to the given receiver cluster.
- the transmit clusters include the aforementioned underlying factors that are related to the transmitter, and the receive clusters include the factors that are related to the receiver, optionally including cross-factors related to both the transmitter and receiver, such as the location of the receiver relative to the location of the transmitter. Note that by mapping individual transmitters and receivers to corresponding transmitter clusters and receiver clusters, the caching complexity is substantially reduced, compared to caching communications among individual transmitter-receiver pairs.
- each cluster is controllable by the user to achieve a desired tradeoff between simulation efficiency and simulation precision.
- each cluster of ‘similar’ factors encompasses a wide range of factors, the number of different factors that need to be simulated and cached are reduced, but the ability to distinguish the individual effects of each factor is correspondingly reduced.
- the range of factors constituting a cluster of ‘similar’ factors is narrow, the effects of each factor that forms a new cluster can be determined, but each of these dis-similar factors must be simulated and cached when they first occur. Additionally, each of these narrowly defined clusters will consume space in the cache.
- FIG. 2 illustrates an example flow diagram of a cache controller for simulating a communication from a transmitter T to a receiver R, in accordance with this invention.
- the transmitter cluster Tc to which the transmitter T belongs is determined. As noted above, this determination may be static or dynamic, including, for example, the current transmit power, the current transmitter location, and so on.
- the receiver cluster Rc to which the receiver R belongs is determined. As also noted above, this determination may also be based on information related to the transmitter T, or the transmitter cluster Tc, such as the receiver's location relative to the transmitter T, such as the aforementioned regions of substantially equal reception characteristics.
- the particular communication is categorized within a finite set (Tc, Rc) of underlying factors, to facilitate the storage and retrieval of characteristics corresponding to each transmitter-receiver cluster in a cache.
- Tc, Rc a finite set of underlying factors
- a four-tuple (Tc′, P, Rc′, G) may be used to categorize the transmission event, wherein Tc′ is a transmit cluster independent of transmit power, P is the transmit power, Rc′ is a receiver cluster independent of receiver zone, and G is the receiver region relative to the location of the transmitter.
- the cache is checked to see if characteristics are currently stored in the cache corresponding to transmitter-receiver clusters Tc, Rc; or, in the alternative example above, corresponding to the four-tuple (Tc′, P, Rc′, G), or whatever categorization of the multiple factors underlying the event is used to facilitate cache management.
- the characteristics of the simulation of an event are referred to as “effects” in FIG. 2 for ease of illustration and understanding, because generally the characteristics of a transmission from a transmitter to receiver correspond to whether the communication is successful, whether a retransmission is to be requested by the receiver, and so on.
- the characteristics may include parameters such as a likelihood of a successful communication, an estimate of bit-error-rate, or other parameters that can subsequently be used to determine the effects of the simulated communication.
- the cache does not contain the characteristics corresponding to a transmission from a transmitter in cluster Tc to a receiver in a cluster Rc. These characteristics may be based on the particular factors of the transmission from transmitter T to receiver R, or based on nominal/quantized factors associated with the clusters Tc and Rc, at 240 .
- the block 240 corresponds to the simulation of a communication from a given transmitter to a given receiver as performed in a conventional simulator.
- the determined characteristics are stored in the cache, as the characteristics associated with a transmission from a transmitter in cluster Tc to a receiver in cluster Rc.
- the cache contains characteristics corresponding to a transmission from a transmitter in cluster Tc to a receiver in a cluster Rc
- the characteristics are retrieved from the cache, at 260 .
- the time required to ‘simulate’ each communication after the first communication from Tc to Rc is dependent upon the time required to retrieve the characteristics from the cache, rather than the time required to actually simulate the characteristics of the communication.
- the simulated movement of each mobile device is relatively slow relative to the transmission rate; thus, the likelihood of a mobile device being repeatedly mapped to the same cluster is relatively high. Therefore, by using this invention, the conventional repeated simulation of the mobile device to determine the effects of each successive communication is avoided and replaced by repeated retrievals of the effects from the cache. Additionally, as noted above, by increasing the range of factors that are mapped to the same cluster, the number of successive communications that are retrieved from the same cache can be increased.
- the characteristics/effects corresponding to the simulation of a communication from transmitter T to receiver R are returned for subsequent processing by the simulation system, regardless of whether the characteristics/effects were conventionally simulated or retrieved from cache. In this manner, the modifications required to a conventional simulator to embody this invention, are minimal.
- FIG. 2 corresponds to a simulation/caching of a transmission from a transmitter to a receiver, and is particularly applicable to the simulation of a wireless network wherein the determination of the characteristics/effects of the transmission is time-consuming
- this invention can be employed for the simulation of any event, provided that the event can be characterized by a finite set of parameters.
- the types of events that are cached are events that typically require substantial time to process to determine the characteristics/effects, compared to the time required to store and retrieve these characteristics/effects in a cache.
- FIG. 3 illustrates an example flow diagram of a simulation system in accordance with this invention, wherein the cache system is not exclusively limited to the simulation/caching of communications in wireless networks.
- the typical flow of a conventional simulator is illustrated in the blocks 310 – 345 ; other simulator-flow processes may also be used.
- the external events that are being simulated to determine the performance of the simulated network are scheduled to occur at given “simulation times”. This simulation time is progressively advanced, at 315 .
- all of the events that have been scheduled to occur at this time are simulated in the loop 320 – 345 .
- the event is retrieved from a scheduler at 325 , then simulated at 330 to determine the effects produced by this event at this time.
- the effects produced by the event generally occur at some defined time after the occurrence of the event.
- These effects are scheduled to be processed by the simulation system at the future simulation-times, at 335 ; these are the aforementioned internally generated effects that are retrieved from the scheduler at 325 at their scheduled simulation times.
- any simulation-specific outputs are provided, such as values to be presented on a simulated timing diagram, values that are stored for subsequent processing by other processes, and so on.
- the loop 320 – 345 is repeated to simulate all events that are scheduled for this simulation-time, and when all of the events for this time are simulated, the flow returns to block 315 , wherein the simulation-time is advanced to the next scheduled externally generated or internally generated event.
- the blocks 350 – 390 illustrate the addition of the principles of this invention to a conventional simulation system's flow 310 – 345 .
- the event is checked, at 350 , to determine if it is a type of event for which caching is provided.
- caching is particularly well suited for events such as the transmission of a communication in a wireless network; however, the principles of this invention can be applied to other simulated events as well.
- the process returns to the conventional simulation flow, at 330 , after clearing a cache-flag, at 390 .
- the event is simulated, and the flow progresses to 385 . Because the cache-flag has been cleared, the process returns to the conventional simulation flow, at 335 .
- the invention allows non-cached events to be processed substantially as they would be in a conventional simulator, and introduces very little overhead to these non-cached events.
- the underlying factors that determine the characteristics/effects of the event are determined at 360 .
- these factors are preferably quantized or categorized for ease of cache management.
- the multiple factors that affect a transmission in a wireless network may be categorized as a transmission from a transmitter of a given transmitter-cluster to a receiver of a given receiver-cluster.
- the processing returns to the conventional simulation flow to simulate the event, at 330 , after setting the cache-flag, at 370 .
- the flow continues at 385 , wherein the cache-flag is checked to determine if this simulated event is a newly simulated cacheable event. If the cache-flag is set, the simulated characteristics/effects of the event are stored in the cache, at 380 , and the process returns to the conventional flow, at 335 .
- the cache is not empty for the given categorized event, indicating that the characteristics/effects of the event have already been determined and stored in the cache, these characteristics/effects are retrieved from the cache, at 375 , and the process returns to the conventional flow, at 335 , thereby bypassing the simulation of the event at 330 . Because of the iterative nature of simulation, if the categorizing of the event at 360 and the subsequent retrieval of the characteristics corresponding to the event at 375 are less time-consuming than the simulation of the event, at 330 , substantial time savings can be achieved.
- conventional cache-management techniques are employed to optimize the performance of the cache and/or to minimize the overhead associated with cache access.
- conventional cache-management techniques are used to manage the size of the cache, including clearing the cache of ‘stale’ information, or infrequently accessed information, to make room for newer information, and so on.
- FIG. 4 illustrates an example block diagram of a simulation system 400 in accordance with this invention.
- the simulation system 400 includes all of the elements of a conventional simulation system, such as input and output components, analysis components, and the like, but only the ‘core’ elements are illustrated in FIG. 4 .
- These core elements are the event handler 410 that processes the scheduled events to determine which nodes to simulate, the node simulator 420 that simulates the event at a node, and the event scheduler 430 that schedules the events produced by the node simulator 430 .
- a cache controller 450 and associated cache memory 460 is provided to intercept the conventional communications between the event handler 410 and the node simulator 420 .
- the cache controller 450 is configured to store the results of a simulation of an initial event having certain underlying factors to the cache memory 460 , and providing these results to the event scheduler 430 from the cache memory 460 whenever another event having the same underlying factors occurs, using, for example, the flow diagram of FIG. 3 , discussed above.
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Description
- a) the word “comprising” does not exclude the presence of other elements or acts than those listed in a given claim;
- b) the word “a” or “an” preceding an element does not exclude the presence of a plurality of such elements;
- c) any reference signs in the claims do not limit their scope;
- d) several “means” may be represented by the same item or hardware or software implemented structure or function;
- e) each of the disclosed elements may be comprised of hardware portions (e.g., including discrete and integrated electronic circuitry), software portions (e.g., computer programming), and any combination thereof;
- f) hardware portions may be comprised of one or both of analog and digital portions;
- g) any of the disclosed devices or portions thereof may be combined together or separated into further portions unless specifically stated otherwise; and
- h) no specific sequence of acts is intended to be required unless specifically indicated.
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EP1774814A1 (en) * | 2004-08-05 | 2007-04-18 | Telecom Italia S.p.A. | Method and apparatus for evaluating the performance of a radiomobile transmission system |
WO2008076505A2 (en) * | 2006-10-27 | 2008-06-26 | Karthikeyan Chandrashekar | Modeling and simulating wireless mac protocols |
US8314736B2 (en) | 2008-03-31 | 2012-11-20 | Golba Llc | Determining the position of a mobile device using the characteristics of received signals and a reference database |
US7800541B2 (en) | 2008-03-31 | 2010-09-21 | Golba Llc | Methods and systems for determining the location of an electronic device |
US9829560B2 (en) | 2008-03-31 | 2017-11-28 | Golba Llc | Determining the position of a mobile device using the characteristics of received signals and a reference database |
US8639270B2 (en) | 2010-08-06 | 2014-01-28 | Golba Llc | Method and system for device positioning utilizing distributed transceivers with array processing |
US9825820B2 (en) * | 2010-12-15 | 2017-11-21 | The Boeing Company | Communication effects in network simulations |
US20130095747A1 (en) | 2011-10-17 | 2013-04-18 | Mehran Moshfeghi | Method and system for a repeater network that utilizes distributed transceivers with array processing |
US9548805B2 (en) | 2012-08-08 | 2017-01-17 | Golba Llc | Method and system for optimizing communication in leaky wave distributed transceiver environments |
US10321332B2 (en) | 2017-05-30 | 2019-06-11 | Movandi Corporation | Non-line-of-sight (NLOS) coverage for millimeter wave communication |
US10484078B2 (en) | 2017-07-11 | 2019-11-19 | Movandi Corporation | Reconfigurable and modular active repeater device |
US10348371B2 (en) | 2017-12-07 | 2019-07-09 | Movandi Corporation | Optimized multi-beam antenna array network with an extended radio frequency range |
US10090887B1 (en) | 2017-12-08 | 2018-10-02 | Movandi Corporation | Controlled power transmission in radio frequency (RF) device network |
US10862559B2 (en) | 2017-12-08 | 2020-12-08 | Movandi Corporation | Signal cancellation in radio frequency (RF) device network |
US10637159B2 (en) | 2018-02-26 | 2020-04-28 | Movandi Corporation | Waveguide antenna element-based beam forming phased array antenna system for millimeter wave communication |
US11088457B2 (en) | 2018-02-26 | 2021-08-10 | Silicon Valley Bank | Waveguide antenna element based beam forming phased array antenna system for millimeter wave communication |
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US5740468A (en) * | 1987-01-12 | 1998-04-14 | Fujitsu Limited | Data transferring buffer |
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US5740468A (en) * | 1987-01-12 | 1998-04-14 | Fujitsu Limited | Data transferring buffer |
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